石墨烯薄膜的化学气相法制备及光、电特性研究

利用化学气相沉积方法制备了石墨烯薄膜,并研究了其光电特性。以乙醇做反应原料、氩气作为携载气体,在873 K、973 K、1 073 K的温度下合成石墨烯薄膜。应用光学显微镜观察,发现在1 073 K时能够制备大面积均匀、平整光滑的石墨烯薄膜。纳曼光谱分析结果表明:制备的石墨烯薄膜出现2 650 cm-1的石墨烯的特征峰-D强峰,同时该峰强度随温度的升高而迅速增强,说明低温不能使沉积的碳原子有效的石墨化为石墨烯,而较高的温度有助于乙醇分解并石墨化为石墨烯薄膜。在1 073 K时沉积的石墨烯薄膜具有良好的光、电特性,其电子迁移率可以达到104 cm2.(V.s)-1,光透射率达97%,因此,可用于制备石墨烯晶体管、太阳能电池等光电子器件。

Study on the growth of honeycomb-like film of basic zinc carbonate induced by bovine serum albumin LB film template

Honeycomb-like films of basic zinc carbonate were successfully prepared on FTO(SnO_(2):F)conductive glass using bovine serum albumin(BSA)as a template at room temperature.After low-temperature annealing,a high-specific-surface-area porous ZnO film with excellent electron mobility was obtained.The surface morphology,crystallization performance,and photoluminescence characteristics of basic zinc carbonate thin films and annealed ZnO thin film were analyzed by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),photoluminescence spectroscopy(PL)and UV-Visible spectroscopy(UV-vis).By comparing with those samples prepared without any protein,it was determined that the complexation between BSA molecules and Zn^(2+)ions was the primary factor in the synthesis of porous films of basic zinc carbonate.The experimental results showed that the ZnO thin film samples prepared with this method had high specific surface area and broadband luminescence characteristics in the near ultraviolet range.

Photo-electrochemical Lithium Insertion Characteristics of Carbon Nanotubes Modified with SrTiO3 Photocatalyst

Perovskite-type SrTiO3 nanoparticles were synthesized by direct hydrolysis-precipitation method and were employed to modify the surface of the carbon nanotubes to form a SrTiO3/CNTs composite. The photoelectrochemical lithium insertion characteristics of the SrTiO3/CNTs composite under xenon light irradiation were investigated. The results show that the light irradiation has little influence on the specific capacity of the CNTs electrode. However, for the SrTiO3/CNTs electrode irradiated by light, the lithium insertion capacity reaches about 251 mAh/g, much higher than that without light irradiation （170 mAh/g）. Cyclic voltammetry test reveals that the light irradiation can remarkably increase the reaction currents of lithium insertion and extraction. This may be attributed to the photo-excited intercalation of Li-ions into the CNTs by the SrTiO3 photocatalyst when irradiated by light.

The Electro-Physical Properties of Rhenium Chalcogenides＇ Thin Films

The electro-physical properties of thin layers of rhenium chalcogenides＇ alloys, their dynamical and static ampere-voltaic characteristics were investigated. During the investigation of static and dynamical ampere-voltaic characteristics of rectifying contact of aluminium and rhenium chalcogenides＇ alloys the switching effects were found.

Silicon Geiger mode avalanche photodiodes

In this letter we present the results regarding the electrical and optical characterization of Geiger mode silicon avalanche photodiodes(GMAP) fabricated by silicon standard planar technology. Low dark count rates,negligible afterpulsing effects,good timing resolution and high quantum detection efficiency in all the visible range have been measured. The very good electro-optical performances of our photodiodes make them attractive for the fabrication of arrays with a large number of GMAP to be used both in the commercial and the scientific fields,as telecommunications and nuclear medical imaging.

Effects of structures of molybdenum catalysts on selectivity in gas-phase propylene oxidation

Molybdenum-based catalysts for the gas-phase oxidation of propylene with air were investigated. Various types of silica-supported molybdenum oxide and molybdenum-bismuth mixed oxide cata- lysts were prepared from inorganic and organometallic molybdenum precursors using wet impregnation and physical vapor deposition methods. The epoxidation activities of the prepared cata- lysts showed direct correlations with their nanostructures, which were identified using transmission electron microscopy. The appearance of a partly or fully crystalline molybdenum oxide phase, which interacted poorly with the silica support, decreased the selectivity for propylene oxide for- mation to below 10%; non-crystalline octahedrally coordinated molybdenum species anchored on the support gave propylene oxide formations greater than 55%, with 11% propylene conversion. Electrochemical characterization of molybdenum oxides with various morphologies showed the importance of structural defects. Direct promotion by bismuth of the epoxidation reactivities over molybdenum oxides is disputed.

Optoelectronic Detecting System for Inner Walls of Pipes

This paper is concerned with a high characteristic image processing and recognition system that is used for inspecting real-time blemishes, streaks and cracks on the inner walls of high accuracy pipes. As a regular detector, the BP neural network is used for extracting features of the image inspected and classifying these images, it takes fully advantage of the function of artificial neural network, such as the information distributed memory, large scale self-adapting parallel processing, high fault-tolerant ability and so forth. Besides, an improved BP algorithm is used in the system for training the network, and making the learning procedure of the net converges to the minimum of overall situation at high rate.

First principles study on electronic structure and optical properties of novel Na-hP4 high pressure phase

The electronic structure and optical properties of novel Na-hP4 high pressure phase at different pressures(260,320,400 and 600 GPa)were investigated by the density functional theory(DFT)with the generalized gradient approximation(GGA)for the exchange and correlation energy.The band structure along the higher symmetry axes in the Brillouin zone,the density of states(DOS) and the partial density of states(PDOS)were presented.The band gap increases and the energy band expands to some extent with the pressure increasing.The dielectric function,reflectivity,energy-loss function,optical absorption coefficient,optical conductivity, refractive index and extinction coefficient were calculated for discussing the optical properties of Na-hP4 high pressure phase at different pressures.

Optoelectronic properties of new functionalized heteroleptic iridium complex

A new functionalized heteroleptic iridium complex coordinated with 1-phenylisoquinoline （1-piq） and a functionalized fl-diketone （G1）, Ir（1-piq）2G1, was synthesized and characterized by 1H-NMR, mass spectrometry and elemental analysis. The larger conjugation of the replacement of acetylacetone （acac） by a functionalizedβ-diketonate ligand led to a significant decrease in the HOMO level toward vacuum level, while Ir（1-piq）2G1 and Ir（1-piq）2（acac） showed red phosphorescent emissions of about 620 nm in dichloromethane solution. The phosphorescent polymer light-emitting devices were achieved, with the complexes incorporated with polyfluorene （PFO） as a host polymer doped with 30% of 5-（4-biphenylyl）-2-（4-tert-butylphenyl）-1,3,4-oxadiazole （PBD） as electron transport material. The energy transfer mechanism of the devices was also discussed. The lower EL performance of Ir（1-piq）2G1 is ascribed to the inter-ligand energy transfer, indicating that it is important to control the energy level of the cyclometalated and ancillary ligands.

Inner Am monium Salt Carbocyanine Filmson SiSurface and Their Photoelectric Properties

Two inner salt carbocyanines were filmed chemically on the Si surface through Si-O-C bond. The structures were characterized by SERS and XPS. And the spectral response and surface photovoltage spectrum were measured. These results show that the Si wafer can be sensitized by dyes, and the filmed Si wafers have photovoltage effect.

Effect of modified starches on depression of diaspore

Four modified starches with selected charge characteristics including cationic starch(CAS),carboxymethyl starch(CMS),amphoteric starch(AMS) and soluble starch(SS) were investigated as depressants for diaspore in reverse flotation test using cationic collector(dodecylamine).Adsorption examination,Zeta potential measurement and Fourier transform infrared(FTIR) spectroscopy were used to clarify the role of the surface charge characteristics of starches in determining the adsorption behavior and depression performance as well as the mineral-starch interaction.Results show that the positively charged starches(CAS and AMS) display higher adsorption amounts and also better depression performance compared with the non-ionic(SS) and anionic starch(CMS),benefiting from the favorable electrostatic attraction with diaspore and also electrostatic repulsion with collector.FTIR spectroscopy proves the presence of hydrogen bonds and chemical complexation between mineral and starches in an integrated manner.

Effect of Film Thickness on Properties of a-Si∶H Films

The a-Si∶H films with different thickness smaller than 1 μm were deposited by plasma enhanced chemical vapor deposition (PECVD) under the optimum deposition conditions. The effect of different thickness on film properties is analyzed.The results show that,with the increase of the film thickness,the dark conductivity, photoconductivity and threshold voltage increase, the optical gap and peak ratio of TA to TO in the Raman spectra decrease, the refractive index keeps almost constant, and the optical absorption coefficient and current ratio of on/off state first maximize and then reduce.

Propagation property of electromagnetic waves in fractal cantor photonic crystals

Two novel structures of fractal Cantor multilayer with defects are presented. The Optical transmission matrix method is used to calculate the transmittance and the reflectance. Compared with the general Cantor multilayer, these novel structures have wider stopbands and show super narrow bands in the middle of the wider stopbands, which can be used as super narrow bandpass filters. The pass band can be less than 0.6 nm near the infrared wavelength of 1530 nm when there is an embedded defect in the cantor multilayer. The optical transmission in the central wavelength is higher than 99 %, which means a very low insert loss. If there are three layers, three super narrow peaks can be found in the middle of the stopband. The central wavelengths are respectively 1232.4 nm, 1372.8 nm and 1538.3 nm. It is much better than other kinds of narrow band filters and it may be used in the optical communications.

Optical and Structural Properties of Carbon Nanotube-Rutile Heterostructures

The paper presents a study of the growth and characterization of carbon nanotube-rutile nanocomposites. The heterostructures were obtained with a chemical mixing method. Scanning electron microscope images show that the samples appear as a homogeneous powder of rutile with carbon nanotubes intercalated in interspaces between the TiO2 grains. Characterization by both X-ray photoelectron spectroscopy and cathodo-luminescence analysis show the formation of CO-Ti chemical bonds with a decrease of 0.8 eV in the band gap compared to pure rutile. The consequence of this band gap modification is a strong change in optical properties. Luminescence emission is drastically reduced and absorption in the visible range is increased of about 6% at very low concentration （1%） of carbon nanotubes.

Insulation System of Power Transformers Behavior Comparison of Mineral Oils and Natural Ester Dielectric Fluids

Paper deals with a comparison of selected properties of several vegetable oil representatives along their accelerated thermal ageing at the temperature of 90 ℃. These properties are compared to two widely used and commercially available mineral transformer oils. A combined insulating system （an oil-paper system） was created with the usage of mentioned oils for measurement purposes. Dissipation factor, capacity and volume resistance are characteristics measured along a thermal ageing of the oil-paper systems. Infrared spectroscopy was used as an additional method. After 1,000 hours of ageing, the dissipation factor of all systems based on vegetable oils did not exceed the value of 0.015. The volume resistance of systems containing mineral oils was approx, twice as high as the volume resistance of those with vegetable oils. The capacity on the other hand was slightly lower in the case of mineral oils application. An experiment also showed that the paper combined with the vegetable oil dries more quickly than in combination with the mineral oil. Infrared spectroscopy has not shown any expressive changes in the chemical structure of aU tested oils yet （up to 1,000 hours of ageing）.

Effect of Substrate Temperature on Optical Characteristics of Silver Island Films for Harvesting Solar Energy

Due to their particular optical characteristics,metallic island films have the potential to significantly increase the energy conversion efficiency of solar cell.We experimentally and theoretically investigated the effect of substrate temperature on the morphologies and optical properties of the silver island films.At low temperature,below 300 ℃,as the substrate temperature increases.Compared to the films prepared at room temperature,the sizes of nanoparticles decrease and the Absorption peaks shift to shorter wavelength accompanied by an increase density resulting in a 150% Absorption efficiency.As the substrate temperature goes up to 300 ℃,nanoparticles with larger in-plan(X-Y)dimensions are formed,the number density decreases and the Absorption peaks redshift but the Absorption efficiency is still 10% higher.Numerical simulation reveals that these behaviors are a consequence of morphologies transformation.

Evaluating Economic and Environmental Benefits of Integrating Solar Photovoltaics within Future Residential Buildings in Saudi Arabia

Renewable energy options, including solar power, are becoming increasingly viable alternatives to conventional sources of energy, such as oil, coal and natural gas. Solar Photovoltaic （PV） technology is one type of solar energy technologies that has recently received substantial attention because it offers the possibility of providing clean power sources for buildings. The aim of this paper is to examine the economic viability of using solar PV within future residential buildings in the oil-rich Saudi Arabia. Strictly speaking, the prospects of using the PV in order to provide 10% of the electricity to be consumed in the houses, which are going to be built in Sandi Arabia over the period 2010-2025, are examined. The study reveals that significant economic and environmental benefits could be realized as a result of such an endeavor.

Evaluation of Heat and Current Characteristics of Bypass Diodes for Fault Detection in Photovoltaic Module

In recent years, PV （photovoltaic） systems have been installed rapidly around the world. However, there is often a delay in the practical application of fault detection in PV systems. In this study, the temperature of BD （bypass diodes） mounted on PV modules was measured for simple and practical fault detection. The temperature of the BD of Module 31 was higher than other modules and a large current passed through one of the BDs. Measuring BD temperatures is easier than other conventional methods of fault detection. From the results of the rise in BD temperature under dark conditions, the increase in temperature increased linearly with increasing current flow. There is a proportional relationship between heat generated and the increasing temperature of the terminal box. The experimental results about surface temperature of the junction box in actual system operation suggested that the electric current through a BD in a terminal box can be known by measuring the surface temperature of the terminal box for PV module fault detection without a system shutdown. Moreover, we tried to evaluate temperature distribution of a terminal box using heat conduction equations. The evaluated results agreed well with the measured results.

Highly sensitive detection of mercury（Ⅱ） ions with few-layer molybdenum disulfide

Two-dimensional （2D） layered transition metal dichalcogenide （TMD） materials （e.g., MoS2） have attracted considerable interest due to their atomically thin geometry and semiconducting electronic properties. With ultrahigh surface to volume ratio, the electronic properties of these atomically thin semiconductors can be readily modulated by their environment. Here we report an investigation of the effects of mercury（II） （Hg^2＋） ions on the electrical transport properties of few-layer molybdenum disulfide （MoS2）. The interaction between Hg^2＋ ions and few-layer MoS2 was studied by field-effect transistor measurements and photoluminescence. Due to a high binding affinity between Hg2. ions and the sulfur sites on the surface of MoS2 layers, Hg^2＋ ions can strongly bind to MoS2. We show that the binding of Hg^2＋ can produce a p-type doping effect to reduce the electron concentration in n-type few-layer MoS2. It can thus effectively modulate the electron transport and photoluminescence properties in few-layer MoS2. By monitoring the conductance change of few-layer MoS2 in varying concentration Hg2~ solutions, we further show that few-layer MoS2 transistors can function as highly sensitive sensors for rapid electrical detection of Hg^2＋ ion with a detection limit of 30 pM.

Fabrication and properties of ultraviolet photo-detectors based on SiC nanowires

A new type of ultraviolet photo-detectors （UVPDs） based on a bundle of highly aligned SiC nanowires was fabricated and the photo-electric properties of the UVPDs including 1-V characteristics and time response were studied in this work. SiC nan- owires were prepared by pyrolysis of a polymer precursor with ferrocene as the catalyst by a CVD route. The diameters of SiC nanowires varied from 100 to 200 nm while they were some centimeters long and the SiC nanowires were with zinc blended cubic form （β-SiC） tested by X-ray diffraction. A bundle of nanowires was fixed onto two legs＇ base by conductive silver paste to form the UVPDs. The electrical measurement of the device showed a significant increase of current when the device was exposed to 254 nm UV light, and the rising time of the device is very short, but the falling time is relatively long. Our results show that the UVPDs based on SiC nanowires have excellent electrical and optical properties which can be potentially applied.